Ovarian Dysgenesis 3 (ODG3) Cell Models for Research

Ovarian Dysgenesis 3 (ODG3) is a rare genetic disorder characterized by primary ovarian insufficiency (POI) and 46,XY partial or complete gonadal dysgenesis. The exact prevalence is unknown, but it is estimated to affect 1 in 100,000 individuals. ODG3 is caused by mutations in the FSHR gene, which encodes the follicle-stimulating hormone receptor. Clinically, patients present with delayed puberty, primary amenorrhea, and hypergonadotropic hypogonadism. There is no cure, and management focuses on hormone replacement therapy and fertility options. The condition has significant psychological and reproductive health impacts.

ODG3 serves as an excellent model for studying FSH signaling, gonadotropin receptor function, and ovarian development. The disorder provides insights into the molecular mechanisms of folliculogenesis and steroidogenesis. Public datasets, such as those from the Genotype-Tissue Expression (GTEx) project and the Human Protein Atlas, offer expression data for FSHR in various tissues. Open questions include the precise downstream signaling pathways affected by specific FSHR mutations and the potential for targeted therapies.

ODG3 is not a cancer, but the FSHR signaling pathway is implicated in ovarian cancer. The major pathways involved in FSHR signaling include:

• • cAMP/PKA pathway: FSH binding to FSHR activates adenylyl cyclase, increasing cAMP levels, which activates protein kinase A (PKA). PKA phosphorylates transcription factors like CREB, regulating genes involved in cell proliferation and differentiation.
• • PI3K/AKT pathway: FSHR activation can also stimulate the PI3K/AKT pathway, promoting cell survival and growth.
• • MAPK/ERK pathway: FSH can activate the MAPK/ERK cascade, leading to cell proliferation and differentiation.

In the context of ovarian dysgenesis, mutations in FSHR disrupt these pathways, leading to impaired follicular development and hormone production.

Data from ClinVar and literature indicate that the most common mutations are missense mutations in the extracellular domain of FSHR, affecting ligand binding.

The deregulated signaling networks in ODG3 primarily involve the FSHR-mediated pathways. Key nodes include:

• • FSHR: G-protein coupled receptor, mutations lead to loss of function.
• • cAMP: Second messenger, reduced levels due to impaired receptor activation.
• • PKA: Kinase, reduced activity.
• • CREB: Transcription factor, reduced phosphorylation.
• • AKT: Kinase, reduced activation.
• • ERK: Kinase, reduced activation.

These disruptions impair granulosa cell proliferation and differentiation, leading to ovarian dysgenesis.

Organoids derived from ovarian tissue can recapitulate folliculogenesis and are useful for studying FSHR function. However, they are more complex and less standardized than cell lines.

• • Genetically engineered mouse models (GEMMs): Fshr knockout mice have been generated and exhibit ovarian dysgenesis, providing a valuable in vivo model.
• • Patient-derived xenografts (PDX): Not commonly used for ODG3 as it is not a cancer.
• • Induced models: Chemical or hormonal induction can mimic some aspects of ovarian failure, but they do not recapitulate the genetic defect.

CRISPR-based gene editing allows the creation of isogenic cell lines with specific FSHR mutations. For example, a FSHR knockout cell line can be generated in KGN or COV434 cells to study loss-of-function effects. Alternatively, a knock-in cell line with a specific pathogenic mutation (e.g., Ala189Val) can be created to model the disease. These models are commercially available and sequence-verified, ensuring reproducibility. They are essential for studying the molecular consequences of FSHR mutations and for drug screening.

Knockout and knock-in cell lines are used to validate the function of FSHR and its variants. For instance, a FSHR knockout cell line can be used to confirm the specificity of FSH signaling inhibitors. Knock-in lines with patient-specific mutations allow the study of genotype-phenotype correlations.

Isogenic pairs (wild-type vs. mutant) are used in high-throughput screens to identify compounds that rescue mutant FSHR function. These models can also be used to test the efficacy of small molecules that act as allosteric modulators of FSHR.

CRISPR-based synthetic lethality screens can identify genes that, when silenced, are lethal in FSHR-mutant cells but not in wild-type cells. This can uncover potential therapeutic targets for ODG3.